Light emitting diodes (LEDs) are widely used in optical displays, traffic lights, data storage, communications, illuminations and medical applications. Current applications of white LEDs include instrument panels of motor vehicles and liquid crystal display (LCD) backlighting. An important goal for white LEDs is to increase the luminosity level to allow replacement of incandescent lamps, because LEDs are smaller, have higher efficiency, and have about a 50 times longer life span, compared to conventional light bulbs.
Conventional white LEDs are usually fabricated according to two methods. In one method, three separate LED chips are enclosed in a single LED body where a red chip, a blue-green chip and a blue chip combine emissions to yield white light. Another widely used method of producing white LEDs entails using a single high-bright blue or UV GaN-based LED chip that has been coated with fluorescent materials, such as phosphors and organic dyes. The use of the fluorescent material introduces reliability problems and energy losses from the conversion of UV or blue photons to yellow or longer-wavelength photons. Also, the packaging step becomes critical for producing consistency in the color characteristic and quality of the LED.
A conventional approach to producing white light-emitting diodes has been explored by Chen et al. (U.S. Pat. No. 6,163,038). This patent describes a white LED and a method of fabricating the white LED that can radiate white light itself by possessing at least two energy bandgaps in the structure of the LED. However, this technology only uses Multiple Quantum Wells (MQW) to get the white emission. Chen et al. only mentions growing the MQWs emitting light with different colors by adjusting growth parameters, not specifying how to achieve it. Chen et al. fails to produce MQWs emitting light continuously covering all the visible range. That is, Chen et al. merely uses a single LED ship to produce light at plural peaks of the spectrum, which are then combined. Thus, it is necessary to use a specific wavelength of light (e.g., 370-500 nm) to serve as a base.
A related art technology for producing enhanced LEDs has been proposed by Chua et al. (U.S. Pat. No. 6,645,885), which pertains to forming indium nitride (InN) and indium gallium nitride (InGaN) quantum dots grown by metal-organic vapor phase epitaxy. This patent describes indium nitride (InN) and indium-rich indium gallium nitride (InGaN) quantum dots embedded in single and multiple InxGa1-xN/InyGa1-yN quantum wells (QWs) formed by using at least one of trimethylindium (TMIn) triethylindium (TEIn) and ethyldimethylindium (EDMIn) as an antisurfactant during MOCVD growth, and the photoluminescence wavelength from these dots ranges from 480 nm to 530 nm. Controlled amounts of TMIn and/or other Indium precursors are important in triggering the formation of dislocation-free quantum dots (QDs), as are the subsequent flows of ammonia and TMIn. This method can be used for the growth of the active layers of blue and green light emitting diodes (LEDs). However, this technology fails to produce a diode that generates white light. White light requires a range of 400 to 750 nm. However, the technology of Chua et al. only covered the lesser wavelength range of 480 nm to 530 nm and could not be used to generate white light.
Accordingly, modern semiconductor and display technology requires new white light-emitting diodes that are easy to construct, have high luminosity and color rendering properties, and have the necessary reliability to establish applications such as light sources for illumination and liquid crystal display devices.